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Novel catalysts derived from hydrotalcite structure and reaction conditions to be used for the selective oxidation of alkylaromatics in supercritical carbon dioxide

A new catalytic system has been developed which is based on Co ion as the active component, dispersed within a matrix made of magnesium-aluminum oxides. This system is particularly suitable for the oxidation of toluene under supercritical conditions by the use of carbon dioxide as the SC solvent. This catalyst type has never been previously described in literature.

Under Supercritical reaction conditions, this catalyst releases Co ions, which then represent the true active sites for the reaction. So, the solid represents a reservoir for the active components. A specific novelty of the system is that it is prepared starting from a hydrotalcite-like precursor; the transformation of the hydrotalcite to the catalyst is achieved by thermal treatment, with development of the system in which Co is dispersed in the magnesia-alumina matrix. This catalyst, while being almost inactive under non-SC conditions, reaches conversion at best of 35% in toluene oxidation with oxygen in SC carbon dioxide, while under comparable temperature, but under non-SC conditions, conversion achieved is far lower than 10%.

The performances are better than literature data of toluene oxidation in SC conditions, although performances should be further improved.

Process and reaction conditions are a determining factor to achieve good conversion and selectivity to benzoic acid in toluene oxidation, or in m-toluic acid starting from m-xylene, with co-production of isophthalic acid.

Reported by

Consorzio Interuniversitario per la Scienza e la Tecnologia dei Materiali, INSTM
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